1. Field of the Invention
The present invention relates to a microwave integrated circuit (IC) used for processing a microwave or millimeter wave signal having a very high frequency of several GHz or higher.
2. Description of the Related Art
Recently, along with the rapid progression of IC techniques, microwave ICs tend to hold an important place in microwave circuits. In such a microwave IC, a circuit having a function of impedance conversion or filtering is constituted by a distributed constant line such as a microstrip line obtained by adhering a metal thin film on a semiconductor substrate.
In the conventional microwave IC, it is convenient if characteristics of the distributed constant line can be externally and electrically adjusted after the manufacture of an IC.
For example, in order to obtain a maximum gain in an IC constituting an amplifier, it is necessary to add an impedance matching circuit for impedance-converting a characteristic impedance (50 106 ) of an externally connected microstrip line into a conjugate complex S.sub.11 * of an S parameter S.sub.11 of an amplification FET. However, FETs suffer from variations in manufacture, and hence, the S parameter also varies. Therefore, a standardized matching circuit cannot realize designed performance. The same also applies to an output matching circuit.